As they work from a short list of leading Republicans, Romney and his advisers say they are weighing whether he should announce his choice some weeks earlier than the traditional time of around the Republican National Convention, which is to be held in Tampa in late August.

The reasoning, advisers say, is that two candidates would be able to raise more money and engage Obama and Vice President Joe Biden in battle with polls showing Americans closely divided on whether to pick the Republican challenger or Democratic incumbent in the November 6 election.

Picking the choice early could also serve to guarantee some positive news coverage at a time when Romney is under fire from Obama over whether he should release more financial information about his wealth.

The subject of when to announce the pick was brought up by a voter at a lively town hall meeting Romney held in a high school gymnasium in Grand Junction, the largest city in western Colorado. The man asked whether Romney would announce his vice presidential choice before the convention.

"I can't give you the timeline for that. That's a decision we'll make down the road. Nor can I give you the individual," said Romney.

Romney is to attend the opening ceremonies of the Summer Olympics in London in two weeks in a trip that will also take him to Jerusalem. Should he choose to name his choice early, then he would have next week as an option for a proper rollout, or he could wait until he returns from abroad and announce his pick in early August.

The Romney campaign refuses to discuss the selection process other than to say Romney is working on it with close confidant Beth Myers.

Romney said his bottom line requirement is his running mate must be "a person who could be president if that were necessary."

His short list is believed to include a host of leading Republicans, including Ohio Senator Rob Portman and former Minnesota Governor Tim Pawlenty, as well as Louisiana Governor Bobby Jindal and Florida Senator Marco Rubio.

Pawlenty and Jindal toured parts of Ohio and Pennsylvania last week to respond to Obama attacks on Romney, while Portman wrote an op-ed piece for an Ohio newspaper. Rubio is to headline a fund-raiser for Romney on Friday. Portman held one for him on Monday.

Romney is also considering whether to name a woman, his wife, Ann, said in a recent CBS interview.

Her comment put the spotlight on New Hampshire Republican Senator Kelly Ayotte, who has been an active surrogate for Romney on the campaign trail but as a first-term senator may lack the experience necessary.

Another prominent Republican woman, former Secretary of State Condoleezza Rice, has said repeatedly she is not interested in serving as the VP choice.

Buffeted daily by attacks from the Obama camp, Romney made clear he was relishing the chance to go toe to toe with Obama in a series of three debates this autumn.

"By the way, I can't wait for the debates to have a chance to go face-to-face with the president," he said.